Method of producing metal nanoparticles and metal nanoparticles produced thereby

ABSTRACT

The present invention relates to a method of producing metal nanoparticles and the metal nanoparticles produced thereby and in particular, to a method of producing metal nanoparticles comprising preparing a first solution including a dispersing stabilizer and a polar solvent; preparing a second solution including a metal precursor and a polar solvent; and adding the second solution into the first solution by dividing at least 2 times. According to the present invention, it is possible to produce metal nanoparticles of uniform size and isotropy with high efficiency using small amount of dispersion stabilizer through controlling reaction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2006-0047267 filed on May 25, 2006, the contents of which are incorporated here by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention relates to a method of producing metal nanoparticles and the metal nanoparticles produced thereby and in particular, to a method of producing metal nanoparticles of uniform size and isotropy at high yield and the metal nanoparticles produced thereby.

2. Description of the Related Art

There are chemical manufacturing method, mechanical manufacturing method and electrical manufacturing method in producing metal nanoparticles. It is difficult to synthesize nanoparticles of high purity and uniform size due to the entrainment of impurity in mechanical process where mechanical power is used in grinding. As to electrical manufacturing method employing electrolysis, the production efficiency is low since the throughput time is long and concentration of particle produced is low. Meantime, there are two major chemical methods of producing metal nanoparticles, namely the vapor method and the colloid method. However, since the vapor method which uses plasma or gas evaporation requires highly expensive equipment, the colloid method by which particles of uniform size can be synthesized at low cost is generally used.

One existing method of producing metal nanoparticles by the colloid method is to dissociate a metal compound in a polar solvent and apply reducing agents or surfactants to produce the metal nanoparticles in the form of a hydrosol. In this method, however, the kinds of dispersing stabilizer used are limited. For example, it has been reported that monomolecular dispersing stabilizer including citrate shows dispersing stability only when the nanoparticle has a size of several nm or less and the particle concentration is low. Macromolecular dispersing stabilizer PVP can disperse nanoparticle of several tens of nm stably in a polar solvent, but it has to be used at concentration of ten weight factor or greater than that of silver precursor to obtain particle of isotropy, i.e., sphere. Moreover, there is a problem that the size of reaction batch has to be increased and the amount of particle produced per a batch is decreased.

SUMMARY

The present invention provides a method of producing metal nanoparticles, by which isotropic metal particles in uniform size can be produced using a polar solvent such as a polyol and small amount of a dispersing stabilizer with a high yield.

Also, the present invention provides metal nanoparticles produced by a method including preparing a first solution including a dispersing stabilizer and a polar solvent; preparing a second solution including a metal precursor and a polar solvent; and adding the second solution by dividing at least 2 times to the first solution.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a virtual graph representing the change in concentration of a dispersing stabilizer and metal ions when a solution including the metal precursor (a second solution) is added into a solution including the dispersing stabilizer (a first solution) at a time.

FIG. 2 is a virtual graph representing the change in concentration of a dispersing stabilizer and metal ions when a solution including the metal precursor (a second solution) is added by dividing 2 times into a solution including the dispersing stabilizer (a first solution).

FIG. 3 is a virtual graph representing the change in concentration of a dispersing stabilizer and metal ions when a solution including the metal precursor (a second solution) is added by dividing several times into a solution including the dispersing stabilizer (a first solution).

FIG. 4 is a SEM image of metal nanoparticles produced according to Example 1 of the invention.

FIG. 5 is a SEM image of metal nanoparticles produced according to Example 2 of the invention.

FIG. 6 is a SEM image of metal nanoparticles produced according to Example 3 of the invention.

FIG. 7 is a SEM image of metal nanoparticles produced according to Example 4 of the invention.

FIG. 8 is a SEM image of metal nanoparticles produced according to Example 5 of the invention.

DETAILED DESCRIPTION

One aspect of the present invention may provide a method of producing metal nanoparticles, comprising:

preparing a first solution including a dispersing stabilizer and a polar solvent;

preparing a second solution including a metal precursor and a polar solvent; and

adding the second solution by dividing at least 2 times to the first solution.

According to an embodiment of the present invention, a dispersing stabilizer may be one or more compounds selected from the group consisting of polyvinylpyrrolidone (PVP), a polyacid and derivatives thereof. Here, the polyacid may be one or more compounds selected from the group consisting of polyacrylic acid, polymaleic acid, polymethylmethacrylate, poly(acrylic acid-co-methacrylic acid), poly(maleic acid-co-acrylic acid) and poly(acrylamide-co-acrylic acid), and the derivatives may be one or more compounds selected from the group consisting of sodium salts, potassium salts and ammonium salts of a polyacid.

The metal precursor may be one or more metal salts selected from the group consisting of AgNO₃, AgBF₄, AgPF₆, Ag₂O, CH₃COOAg, AgCF₃SO₃, AgClO₄, AgCl, Ag₂SO₄, CH₃COCH═COCH₃Ag, Cu(NO₃)₂, CuCl₂, CuSO₄, C₅H₇CuO₂, NiCl₂, Ni(NO₃)₂, NiSO₄ and HAuCl₄.

The polar solvent used for preparing the first solution and the second solution may be, independently, one or more solvents selected from the group consisting of water, an alcohol and a polyol. Here, the alcohol may be one or more alcohols selected from the group consisting of methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, hexanol and octanol. And the polyol may be one or more ones selected from the group consisting of glycerol, glycol, ethylene glycol, diethylene glycol, triethyleneglycol, butanediol, tetraethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol and 1,2-hexadiol.

According to the present invention, 200 to 10,000 parts by weight of the polar solvent of the first solution may be mixed based to 100 parts by weight of the dispersing stabilizer, and 150 to 100,000 parts by weight of the polar solvent of the second solution may be mixed based to 100 parts by weight of the metal precursor.

The first solution according to the present invention may further include one or more solid catalysts selected from the group consisting of Cu (II), Cu (I), Fe (III) and Fe (II). Here, 1 to 10 parts by weight of the solid catalyst is mixed based to 100 parts by weight of the metal precursor.

Also, the second solution according to the present invention may further include one or more reducing agents selected from the group consisting of dimethylformamide (DMF), dimethyl sulfuroxide (DMSO), NaBH₄, LiBH₄, tetrabutylammonium borohydride, N₂H₄ and the mixtures thereof. Here, 1 to 10 parts by weight of the reducing agent is mixed based to 100 parts by weight of the metal precursor.

The rate of adding the second solution into the first solution is 0.001 to 1 mole of the metal precursor to 1 mole of the dispersing stabilizer per minute.

In the meantime, adding the second solution into the first solution is performed at 120 to 190° C.

A method of producing metal nanoparticles of the present invention may further include:

washing the mixture of the second solution and the first solution with an organic solvent after the adding step; and

obtaining the metal nanoparticles through centrifuging the mixture of the second solution and the first solution.

Another aspect of the invention may provide metal nanoparticles produced by a method including preparing a first solution including a dispersing stabilizer and a polar solvent; preparing a second solution including a metal precursor and a polar solvent; and adding the second solution by dividing at least 2 times to the first solution.

Here, the content of the dispersing stabilizer combined with the metal nanoparticles may be 2 to 8 wt %.

Hereinafter, the method of producing metal nanoparticles and the metal nanoparticles thus produced according to the present invention will be described in detail, taken in conjunction with the accompanying drawings.

It is very important to select a metal precursor, a dispersing stabilizer, a solvent and an additional reducing agent for producing metal nanoparticles in uniform size at high concentration. The combination of such components, reaction temperature and reaction time can have an effect on the nucleation and growth of nanoparticles.

According to the nucleation and growth model, the nucleus, generated in the initial stage, with a size of less than critical value is unstable and redissolved into a solvent; but the nucleus with a size of larger than critical value is stable, and thus nucleation occurs. This critical value is generally determined dependent on the amount of a precursor and a dispersing stabilizer. According to this theory, while a great amount of a precursor allows particles of uniform size to form in the initial stage, as the reaction progresses; the degree of particle size distribution becomes larger and larger because of the reduced concentration of a precursor (Alivisatos et al, and the Nature 2005). Therefore, in order to make particle of uniform size, it is considered that the concentration of a precursor and the ratio of a precursor and dispersing stabilizer are important in the reaction.

In addition, the study on the synthesis of silver nanoparticles of Xia et al. has shown that initial nucleation has a large effect on the shape of particles produced finally. That is, nanoparticles of sphere form can be formed only when it has the form of near-sphere in the initial nucleation stage. At this time, it has shown that the molar ratio of a dispersing stabilizer, polyvinylpyrrolidone (PVP) to a silver precursor had to be over the factor of 10, and anisotropic particles were eventually formed using PVP of over the factor of 15 (Xia et al, and the Chem. Eur. J. 2005).

As described above, in order to produce metal nanoparticles of sphere form and uniform size, the use of a great amount of a dispersing stabilizer is required, which results in augmentation in size of a reaction batch, and thus reduction in yield of particle synthesis per a reaction batch.

Therefore, the present inventor tried to provide a method of producing metal nanoparticles of uniform size and isotropy with high efficiency through controlling reaction in mixing a dispersing stabilizer and a metal precursor.

Another aspect of the present invention may provide a method of producing metal nanoparticles, including:

preparing a first solution including a dispersing stabilizer and a polar solvent;

preparing a second solution including a metal precursor and a polar solvent; and

adding the second solution by dividing at least 2 times to the first solution.

As shown in FIG. 1, when the second solution including a metal precursor is added into the first solution including a dispersing stabilizer at a time, the amount of the dispersing stabilizer forming complex with metal ions will be smaller, while the amount of the dispersing stabilizer existing independently will be greater as the reaction progresses. As a result, the dispersing stabilizer remaining after stabilizing nanoparticles is discarded.

However, as shown in FIG. 2, when a second solution including a metal precursor is added by dividing 2 times into the first solution, the real equivalent ratio of the dispersing stabilizer to the metal precursor becomes 2 fold, which is advantageous for forming isotropic particles. As shown in FIG. 3, when a second solution is added by dividing several times into the first solution, the real equivalent ratio of the dispersing stabilizer to the metal precursor approaches close to infinity. Thus, according to the present invention, even if the amount of the dispersing stabilizer being added is decreased, the real equivalent ratio of the dispersing stabilizer to the metal precursor can be maintained over the factor of ten, and isotropic metal nanoparticles can be obtained with high efficiency.

According to an embodiment of the present invention, the dispersing stabilizer may be one or more selected from the group consisting of polyvinylpyrrolidone (PVP), a polyacid and the derivatives thereof. Here, the polyacid may be a polymer having carboxyl group or the derivative thereof in the main chain or side chain and the degree of polymerization of 10 to 100,000. Examples of the polyacid may include polyacrylic acid, polymaleic acid, polymethylmethacrylate, poly (acrylic acid-co-methacrylic acid), poly(maleic acid-co-acrylic acid), poly(acrylamide-co-acrylic acid) and etc. but it is not limited thereto.

The derivative of a polyacid is referred to a compound wherein hydrogen atoms in the carboxyl group of the polyacid are substituted with other atoms or molecules, and may be sodium salts, potassium salts and ammonium salts of the polyacid.

In the present invention, the metal forming metal nanoparticles is not limited particularly, but may include gold, silver, copper, nickel, palladium and etc. As to the metal precursor providing metal ions which can be reduced to metal nanoparticles, the salts of these metals can be used. These metal salts may be one or more selected from the group consisting of AgNO₃, AgBF₄, AgPF₆, Ag₂O, CH₃COOAg, AgCF₃SO₃, AgClO₄, AgCl, Ag₂SO₄, CH₃COCH═COCH₃Ag, Cu(NO₃)₂, CuCl₂, CuSO₄, C₅H₇CuO₂, NiCl₂, Ni(NO₃)₂, NiSO₄ and HAuCl₄, but are not limited thereto.

The polar solvent used for preparing a first solution and a second solution is not limited particularly, if it is generally used in the art, and may include water, alcohol, a polyol and the mixture thereof. This polar solvent plays a role as a reducing agent which reduces a metal ion to form a metal particle.

Here, examples of the alcohol may include methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, hexanol and octanol etc., but is not limited thereto.

The polyol is referred to a water soluble polymer of low molecular weight having a plurality of hydroxyl group, and diol. Examples of the polyol may include glycerol, glycol, ethylene glycol, diethylene glycol, triethyleneglycol, butanediol, tetraethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol and 1,2-hexadiol etc., but is not limited thereto.

According to the present invention, 200 to 10,000 parts by weight of the polar solvent may be mixed based to 100 parts by weight of the dispersing stabilizer in preparing the first solution. When less than 200 parts by weight of the polar solvent is used, complete dissolution of the dispersing stabilizer is not accomplished, and when more than 10,000 parts by weight of the polar solvent is used, the reactor volume has to be increased and thus productivity is decreased.

Also, 150 to 100,000 parts by weight of the polar solvent may be mixed based to 100 parts by weight of the metal precursor in preparing the second solution. When less than 150 parts by weight of the polar solvent is used, complete dissolution of the metal precursor is not accomplished, and when more than 100,000 parts by weight of the polar solvent is used, the reactor volume has to be increased and thus productivity is decreased.

In addition, the first solution and the second solution may further include additives such as catalysts or reducing agents in order to control nucleation and reaction rate.

The first solution according to the present invention may further include one or more solid catalysts selected from the group of consisting of Cu(II), Cu(I), Fe(III) and Fe(II). Here, 1 to 10 parts by weight of the solid catalyst may be added based to 100 parts by weight of the metal precursor.

The second solution according to the present invention may further include one or more reducing agents selected from the group consisting of dimethylformamide (DMF), dimethyl sulfuroxide (DMSO), NaBH₄, LiBH₄, tetrabutylammonium borohydride, N₂H₄ and the mixtures thereof. Here, 1 to 10 parts by weight of the reducing agent may be added based to 100 parts by weight of the metal precursor.

After the first solution and the second solution are prepared in this way, the second solution is added into the first solution by dividing at least 2 times. In adding the second solution into the first solution, any typical adding method may be used. Preferably, the second solution can be consecutively added into the first solution with agitation through a metal precursor feeder. At this time, the rate of adding the second solution into the first solution is 0.001 to 1 mole of the metal precursor to 1 mole of the dispersing stabilizer per minute. This is because the addition rate of the range is effective in nucleation and formation of isotropic nanoparticles.

Further, the step wherein the second solution is added into the first solution may be performed at 120 to 190° C. Raising temperature to the range described above from the boiling point or lower of the polar solvent makes reduction reaction occur. Meanwhile, in case of raising temperature while agitating the mixed solution including the first solution and the second solution, temperature is raised at a fixed rate to the range of temperature described above, so that nanoparticles of uniform size are formed, which is advantageous for the size control of particles. If a reducing agent is added, the reaction can be performed at a lower temperature than when a reducing agent is not added.

As the first solution and the second solution are mixed and metal particles begin to form in this way, the color of the mixed solution begins to change into a red, and then as the metal nanoparticles begin to grow up to nano size, it changes into a dark green. Since the size of the metal particles being grown can be determined through the change in metal peaks in UV-Vis spectra, the reaction can be stopped by investigating the color change if particles of desired size are formed.

The reaction time to form nanoparticles can be varied e.g., 1 to 60 minutes, with the mixing ratio of the components, temperature condition and the presence of a reducing agent. If it is over 60 minutes, the size of particles formed is too large.

After producing the metal nanoparticles as described above, the nanoparticles can be obtained from the reaction solution through the methods generally used in the art.

Thus, a method of producing metal nanoparticles of the present invention may further comprise:

washing the reaction mixture with an organic solvent after the step of adding of the second solution into the first solution; and

obtaining the metal nanoparticles through centrifuging the reaction mixture.

In the step of washing, methanol, ethanol, MDF or the mixture thereof can be used as the organic solvent.

Further, a method of producing metal nanoparticles of the present invention may comprise drying the metal nanoparticles obtained. The metal nanoparticles produced according to the method of the present invention can be uniformly dispersed by a dispersing stabilizer and thereby be grown uniformly without coagulation, and can be also obtained in the form of isotropic nano particles. Here, the content of the dispersing stabilizer combined with the metal nanoparticles may be 2 to 8 wt % of total weight of the metal nanoparticles produced.

Hereinafter, the present invention is described in further detail by example. The following examples are intended to further illustrate the present invention without limiting its scope.

EXAMPLE 1

After mixing 300 parts by weight of ethylene glycol and 100 parts by weight of polyvinylpyrrolidone (PVP) with agitation, the solution prepared (a first solution) was heated to 170° C. 100 parts by weight of AgNO₃ and 250 parts by weight of ethylene glycol were mixed to prepare a second solution. The second solution was added into the first solution through a fluid controller with an addition rate where a molar ratio of silver ions to total amount of PVP per minute was 0.4, and the result solution was reacted for 20 minutes. After the solution turned into an emerald green, it was washed with acetone/methanol mixture and centrifuged to obtain silver nanoparticles.

EXAMPLE 2

The silver nanoparticles were obtained from performing identical processes as in example 1 except that the reaction temperature was 150° C., the addition rate was 0.2 molar ratio per minute and the reaction time was 30 minutes.

EXAMPLE 3

After mixing 400 parts by weight of ethylene glycol and 100 parts by weight of polyvinylpyrrolidone (PVP) with agitation, the solution prepared (a first solution) was heated to 150° C. 100 parts by weight of AgNO₃ and 300 parts by weight of ethylene glycol were mixed to prepare a second solution. The second solution was added into the first solution through a fluid controller with an addition rate where a molar ratio of silver ions to total amount of PVP per minute was 0.07, and the result solution was reacted for 60 minutes. After the solution turned into an emerald green, it was washed with acetone/methanol mixture and centrifuged to obtain silver nanoparticles.

EXAMPLE 4

After mixing 400 parts by weight of ethylene glycol, 100 parts by weight of polyvinylpyrrolidone (PVP) and 6 parts by weight of Cu(II) with agitation, the solution prepared (a first solution) was heated to 160° C. 100 parts by weight of AgNO₃, 100 parts by weight of DMF and 100 parts by weight of ethylene glycol were mixed to prepare a second solution. The second solution was added into the first solution through fluid a controller with an addition rate where a molar ratio of silver ions to total amount of PVP per minute was 0.2, and the result solution was reacted for 60 minutes. After the solution turned into an emerald green, it was washed with acetone/methanol mixture and centrifuged to obtain silver nanoparticles.

EXAMPLE 5

The silver nanoparticles were obtained from performing identical processes as in example 4 except that Cu(II) catalyst was not used, the reaction temperature was 150° C., the addion rate was 0.2 molar ratio per minute and the reaction time was 15 minutes.

FIGS. 4 to 8 are SEM images of metal nanoparticles produced according to example 1 to 5 of the present invention. Referring to FIGS. 4 to 8, isotropic silver nanoparticles of average 20 to 60 nm were produced according to the present invention. Moreover, in case of adding a metallic catalyst and a reducing agent as in Example 4, nucleation occurs fast, and nanoparticles having uniform size of about 10 nm can be produced. In the meantime, in case the molar ratio of PVP to silver ions is large as in Example 5, total yield is high in spite of a short reaction time.

It will be understood that various details of the presently disclosed subject matter can be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.

INDUSTRIAL APPLICABILITY

According to the present invention, a method of producing metal nanoparticles of uniform size and isotropy with high efficiency using small amount of dispersion stabilizer through controlling reaction is provided, and it is useful in the synthesis of metal nanoparticles produced in colloid system. 

1. A method of producing metal nanoparticles, comprising: preparing a first solution including a dispersing stabilizer and a polar solvent; preparing a second solution including a metal precursor and a polar solvent; and adding the second solution by dividing at least 2 times into the first solution.
 2. The method of claim 1, wherein the dispersing stabilizer is one or more compounds selected from the group consisting of polyvinylpyrrolidone (PVP), a polyacid and derivatives thereof.
 3. The method of claim 2, wherein the polyacid is one or more compounds selected from the group consisting of polyacrylic acid, polymaleic acid, polymethylmethacrylate, poly(acrylic acid-co-methacrylic acid), poly(maleic acid-co-acrylic acid) and poly(acrylamide-co-acrylic acid), and the derivative is one or more compounds selected from the group consisting of sodium salts, potassium salts and ammonium salts of the polyacid.
 4. The method of claim 1, wherein the metal precursor is a compound selected from the group consisting of AgNO₃, AgBF₄, AgPF₆, Ag₂O, CH₃COOAg, AgCF₃SO₃, AgClO₄, AgCl, Ag₂SO₄, CH₃COCH═COCH₃Ag, Cu(NO₃)₂, CuCl₂, CuSO₄, C₅H₇CuO₂, NiCl₂, Ni(NO₃)₂, NiSO₄ and HAuCl₄.
 5. The method of claim 1, wherein the polar solvent used for preparing the first solution and the second solution is independently one or more solvent selected from the group consisting of water, an alcohol and a polyol.
 6. The method of claim 5, wherein the alcohol is one or more alcohols selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, hexanol and octanol.
 7. The method of claim 5, wherein the polyol is one or more polyols selected from the group consisting of glycerol, glycol, ethylene glycol, diethylene glycol, triethyleneglycol, butanediol, tetraethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol and 1,2-hexadiol.
 8. The method of claim 1, wherein 200 to 10,000 parts by weight of the polar solvent of the first solution is mixed based to 100 parts by weight of the dispersing stabilizer.
 9. The method of claim 1, wherein 150 to 100,000 parts by weight of the polar solvent of the second solution is mixed based to 100 parts by weight of the metal precursor.
 10. The method of claim 1, wherein the first solution further includes one or more solid catalysts selected from the group consisting of Cu (II), Cu (I), Fe (III) and Fe (II).
 11. The method of claim 10, wherein 1 to 10 parts by weight of the solid catalyst is mixed based to 1.00 parts by weight of the metal precursor.
 12. The method of claim 1, wherein the second solution further includes one or more reducing agents selected from the group consisting of dimethylformamide (DMF), dimethyl sulfuroxide (DMSO), NaBH₄, LiBH₄, tetrabutylammonium borohydride, N₂H₄ and the mixtures thereof.
 13. The method of claim 12, wherein 1 to 10 parts by weight of the reducing agent is mixed based to 100 parts by weight of the metal precursor.
 14. The method of claim 1, wherein an addition rate of the second solution ranges from 0.001 to 1 mole of the metal precursor to 1 mole of dispersing stabilizer per minute.
 15. The method of claim 1, wherein the addition step is performed at 120 to 190° C.
 16. The method of claim 1, wherein the method of producing metal nanoparticles, further comprise: washing the mixture with an organic solvent after the step of adding the second solution into the first solution; and obtaining the metal nanoparticles through centrifuging the mixture.
 17. Metal nanoparticles, produced by a method comprising preparing a first solution including a dispersing stabilizer and a polar solvent; preparing a second solution including a metal precursor and a polar solvent; and adding the second solution into the first solution by dividing at least 2 times.
 18. The metal nanoparticles of claim 17, including 2 to 8 weight % dispersing stabilizers among the metal nanoparticles. 